Dislocation density and sub-grain size evolution of 2CrMoNiWV during low cycle fatigue at elevated temperatures

We present the dislocation density and sub-grain size evolution for samples subjected to low cycle fatigue (LCF) loading under various conditions. Interrupted LCF tests have been performed on a cyclic softening bainitic steam turbine rotor steel, 2CrMoNiWV, at total strain amplitudes of ±0.25%, ±0.4% and ±0.7%, strain rates of 0.01 and 0.1% s−1, and temperatures of 500 and 565 °C. Neutron diffraction experiments have been carried out on these samples, which were evaluated by means of a convolutional multiple whole profile peak shape analysis approach. With this analysis, both dislocation density and sub-grain size evolutions have been determined and compared to the results of transmission electron microscopy (TEM) and scanning TEM (STEM) spot-check evaluations. In addition, the proportions of prevailing dislocation types and the correlation factor of the microstructure have been determined. Finally, the results have been used to establish a phenomenological model describing the relationships between the observed cyclic softening and the evolution characteristics of dislocation density and sub-grain size, as a function of strain amplitude, strain rate and temperature.